JP4412326B2 - Balanced SAW filter - Google Patents

Balanced SAW filter Download PDF

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JP4412326B2
JP4412326B2 JP2006542921A JP2006542921A JP4412326B2 JP 4412326 B2 JP4412326 B2 JP 4412326B2 JP 2006542921 A JP2006542921 A JP 2006542921A JP 2006542921 A JP2006542921 A JP 2006542921A JP 4412326 B2 JP4412326 B2 JP 4412326B2
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idt
saw filter
coupled resonator
balanced
longitudinally coupled
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JPWO2006049000A1 (en
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裕一 高峰
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Murata Manufacturing Co Ltd
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/64—Filters using surface acoustic waves
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H03H9/14544—Transducers of particular shape or position
    • H03H9/14576—Transducers whereby only the last fingers have different characteristics with respect to the other fingers, e.g. different shape, thickness or material, split finger
    • H03H9/14582—Transducers whereby only the last fingers have different characteristics with respect to the other fingers, e.g. different shape, thickness or material, split finger the last fingers having a different pitch
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/0023—Balance-unbalance or balance-balance networks
    • H03H9/0028—Balance-unbalance or balance-balance networks using surface acoustic wave devices
    • H03H9/0047—Balance-unbalance or balance-balance networks using surface acoustic wave devices having two acoustic tracks
    • H03H9/0052—Balance-unbalance or balance-balance networks using surface acoustic wave devices having two acoustic tracks being electrically cascaded
    • H03H9/0057—Balance-unbalance or balance-balance networks using surface acoustic wave devices having two acoustic tracks being electrically cascaded the balanced terminals being on the same side of the tracks
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/0023—Balance-unbalance or balance-balance networks
    • H03H9/0028—Balance-unbalance or balance-balance networks using surface acoustic wave devices
    • H03H9/0047—Balance-unbalance or balance-balance networks using surface acoustic wave devices having two acoustic tracks
    • H03H9/0052—Balance-unbalance or balance-balance networks using surface acoustic wave devices having two acoustic tracks being electrically cascaded
    • H03H9/0061—Balance-unbalance or balance-balance networks using surface acoustic wave devices having two acoustic tracks being electrically cascaded the balanced terminals being on opposite sides of the tracks
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H03H9/14544—Transducers of particular shape or position
    • H03H9/14588—Horizontally-split transducers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/25—Constructional features of resonators using surface acoustic waves

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
  • Thermistors And Varistors (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
  • Harvester Elements (AREA)
  • Gyroscopes (AREA)

Abstract

A SAW filter having a balanced-unbalanced converting function allows for a less effect of direct waves on electric signals transmitted to balanced terminals through wiring lines. In a balanced SAW filter (1), a third IDT (13) of a first SAW filter element (3) has first and second IDT segments (13a and 13b), and likewise, an eighth IDT (18) of a second SAW filter element 4 has first and second IDT segments (18a and 18b). A first IDT (11), the first IDT segment (13a), the second IDT segment (13b), and a fifth IDT (15) included in the first SAW filter element (3) are respectively connected to a sixth IDT (16), the first IDT segment (18a), the second IDT segment (18b), and a tenth IDT segment (20) included in the second SAW filter element (4) by means of first to fourth wiring lines (31 to 34). The phase of electric signals transmitted through the first and third wiring lines (31 and 33) differs from the phase of electric signals transmitted through the second and fourth wiring lines (32 and 34) by 180°.

Description

本発明は、平衡−不平衡変換機能を有するバランス型ＳＡＷフィルタに関し、特に、５ＩＤＴ型の第１，第２の縦結合共振子型ＳＡＷフィルタ部が二段縦続接続された構造を有するバランス型ＳＡＷフィルタに関する。   The present invention relates to a balanced SAW filter having a balanced-unbalanced conversion function, and more particularly, a balanced SAW filter having a structure in which 5IDT type first and second longitudinally coupled resonator type SAW filter units are cascaded in two stages. Regarding filters.

例えば携帯電話機などの移動体通信機器において、帯域フィルタとして、弾性表面波（ＳＡＷ）フィルタが広く用いられている。特に、携帯電話機などの小型化及び高性能化にともなって、アンテナ端子に接続されるＲＦ段の帯域フィルタとして、平衡−不平衡変換機能を有する、いわゆるバランス型ＳＡＷフィルタが用いられてきている。この種のバランス型ＳＡＷフィルタの一例が、下記の特許文献１に開示されている。   For example, surface acoustic wave (SAW) filters are widely used as bandpass filters in mobile communication devices such as cellular phones. In particular, with the miniaturization and high performance of cellular phones and the like, so-called balanced SAW filters having a balanced-unbalanced conversion function have been used as RF stage band-pass filters connected to antenna terminals. An example of this type of balanced SAW filter is disclosed in Patent Document 1 below.

図３に示すように、特許文献１に記載のバランス型ＳＡＷフィルタ１００では、第１，第２の縦結合共振子型ＳＡＷフィルタ部１０１，１０２が縦続（カスケード）接続されている。第１の縦結合共振子型ＳＡＷフィルタ部１０１は、表面波伝搬方向に沿って配置された第１〜第５のＩＤＴ１１１〜１１５を有する。ＩＤＴ１１１〜１１５が設けられている領域の表面波伝搬方向両側には、反射器１１６，１１７が配置されている。   As shown in FIG. 3, in the balanced SAW filter 100 described in Patent Document 1, first and second longitudinally coupled resonator SAW filter units 101 and 102 are connected in cascade (cascade). The first longitudinally coupled resonator-type SAW filter unit 101 includes first to fifth IDTs 111 to 115 arranged along the surface wave propagation direction. Reflectors 116 and 117 are arranged on both sides of the surface wave propagation direction of the region where the IDTs 111 to 115 are provided.

同様に、第２の縦結合共振子型ＳＡＷフィルタ１０２は、表面波伝搬方向に沿って配置された第６〜第１０のＩＤＴ１２１〜１２５と、反射器１２６，１２７とを有する。   Similarly, the second longitudinally coupled resonator type SAW filter 102 includes sixth to tenth IDTs 121 to 125 arranged along the surface wave propagation direction, and reflectors 126 and 127.

ここでは、第２，第４のＩＤＴ１１２，１１４の一端が共通接続され、不平衡端子１３１に接続されている。また、第１，第３，第５のＩＤＴの一端が共通接続されている。第１のＩＤＴ１１１の他端は、第１の配線ライン１４１により、第６のＩＤＴ１２１に接続されている。同様に、第３，第５のＩＤＴ１１３，１１５は、第２，第３の配線ライン１４２，１４３により、第８，第１０のＩＤＴ１２３，１２５に接続されている。他方、第７のＩＤＴ１２２の一端が、第１の平衡端子１３２に接続されており、ＩＤＴ１２２の他端は、ＩＤＴ１２４の一端と共通接続されている。ＩＤＴ１２４の他端が第２の平衡端子１３３に接続されている。特許文献１に記載のＳＡＷフィルタ１００では、上記構成を有するため、小型化を進めることができ、かつ挿入損失を小さくし得るとされている。
特開２０００−９１８８３号公報 Here, one ends of the second and fourth IDTs 112 and 114 are commonly connected and connected to the unbalanced terminal 131. One ends of the first, third, and fifth IDTs are commonly connected. The other end of the first IDT 111 is connected to the sixth IDT 121 by a first wiring line 141. Similarly, the third and fifth IDTs 113 and 115 are connected to the eighth and tenth IDTs 123 and 125 by the second and third wiring lines 142 and 143, respectively. On the other hand, one end of the seventh IDT 122 is connected to the first balanced terminal 132, and the other end of the IDT 122 is commonly connected to one end of the IDT 124. The other end of the IDT 124 is connected to the second balanced terminal 133. Since the SAW filter 100 described in Patent Document 1 has the above-described configuration, it can be reduced in size and insertion loss can be reduced.
JP 2000-91883 A

しかしながら、バランス型ＳＡＷフィルタ１００では、５ＩＤＴ型の縦結合共振子型ＳＡＷフィルタ部１０１，１０２が縦続接続されているが、上記第１〜第３の配線ライン１４１〜１４３に、同位相の信号が流れることとなる。   However, in the balanced SAW filter 100, 5IDT type longitudinally coupled resonator type SAW filter units 101 and 102 are connected in cascade, but signals having the same phase are transmitted to the first to third wiring lines 141 to 143. It will flow.

他方、第２の平衡端子１３３と第９のＩＤＴ１２４とを電気的に接続している配線ライン１４４は、図３に示すように、第２，第３の配線ライン１４２，１４３の間から第１，第２の配線ライン１４１，１４２が設けられている部分を越えて外側に引き出されている。また、第１の平衡端子１３２と第７のＩＤＴ１２２とを接続している配線ライン１４５は、第１〜第３の配線ライン１４１〜１４３が設けられている領域とは隔てられた領域に配置されている。   On the other hand, the wiring line 144 that electrically connects the second balanced terminal 133 and the ninth IDT 124 is first between the second and third wiring lines 142 and 143 as shown in FIG. , The second wiring lines 141 and 142 are drawn out beyond the portion. In addition, the wiring line 145 connecting the first balanced terminal 132 and the seventh IDT 122 is disposed in a region separated from the region where the first to third wiring lines 141 to 143 are provided. ing.

従って、第１〜第３の配線ライン１４１〜１４３と第１，第２の平衡端子１３２，１３３との間の浮游容量に基づく直達波が大きく、この大きな直達波が平衡端子１３２，１３３に加わっていた。また、平衡端子１３３に加わる直達波の大きさが、平衡端子１３２に加わる直達波の大きさよりもかなり大きくならざるを得なかった。そのため、平衡端子１３２，１３３間の平衡度が悪いという問題があった。   Therefore, a direct wave based on the floating capacity between the first to third wiring lines 141 to 143 and the first and second balanced terminals 132 and 133 is large, and this large direct wave is applied to the balanced terminals 132 and 133. It was. Further, the magnitude of the direct wave applied to the balanced terminal 133 has to be considerably larger than the magnitude of the direct wave applied to the balanced terminal 132. Therefore, there is a problem that the balance between the balanced terminals 132 and 133 is poor.

本発明の目的は、上述した従来技術の欠点を解消し、５ＩＤＴ型の第１，第２の縦結合共振子型ＳＡＷフィルタ部を二段縦続接続してなるバランス型ＳＡＷフィルタにおいて、小型化及び挿入損失の低減を図り得るだけでなく、２つの平衡端子に加わる直達波の影響を低減することが可能とされているバランス型ＳＡＷフィルタを提供することにある。   An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to reduce the size and size of a balanced SAW filter in which 5IDT type first and second longitudinally coupled resonator type SAW filter units are cascade-connected in two stages. An object of the present invention is to provide a balanced SAW filter that can not only reduce insertion loss but also reduce the influence of direct waves applied to two balanced terminals.

本発明は、不平衡端子と、第１，第２の平衡端子とを有するバランス型ＳＡＷフィルタであって、圧電基板と、前記圧電基板上に形成されており、表面波伝搬方向に沿って配置された第１〜第５のＩＤＴとを備え、前記第２，第４のＩＤＴが不平衡端子に接続されており、中央の第３のＩＤＴが、一対のバスバーの内の一方のバスバーを分割することにより設けられた第１，第２の分割ＩＤＴ部を有する第１の縦結合共振子型ＳＡＷフィルタ部と、前記圧電基板上において、表面波伝搬方向に沿って配置された第６〜第１０のＩＤＴを有し、前記第７，第９のＩＤＴがそれぞれ第１，第２の平衡端子に接続されており、中央の第８のＩＤＴが、一対のバスバーの内の一方のバスバーを分割することにより設けられた第１，第２の分割ＩＤＴ部を有する第２の縦結合共振子型ＳＡＷフィルタ部とを備え、前記第１のＩＤＴと、第６のＩＤＴとを接続している第１の配線ラインと、前記第３のＩＤＴの第１の分割ＩＤＴ部と、第８のＩＤＴの第１の分割ＩＤＴ部を接続している第２の配線ラインと、前記第３のＩＤＴの第２の分割ＩＤＴ部と、第８のＩＤＴの第２の分割ＩＤＴ部とを接続している第３の配線ラインと、前記第５のＩＤＴと第１０のＩＤＴとを接続している第４の配線ラインとをさらに備え、前記第１，第３の配線ラインを伝送している電気信号の位相と、前記第２，第４の配線ラインを伝送する電気信号の位相とが１８０度異なるように第１〜第１０のＩＤＴが設けられていることを特徴とする。   The present invention is a balanced SAW filter having an unbalanced terminal and first and second balanced terminals, which is formed on the piezoelectric substrate and the piezoelectric substrate, and is arranged along the surface wave propagation direction. The first and fifth IDTs are connected to the unbalanced terminal, and the third IDT in the center divides one bus bar of the pair of bus bars. And a first longitudinally coupled resonator type SAW filter section having first and second divided IDT sections, and sixth to sixth sections arranged along the surface wave propagation direction on the piezoelectric substrate. 10 IDTs, the seventh and ninth IDTs are connected to the first and second balanced terminals, respectively, and the middle eighth IDT divides one bus bar of the pair of bus bars 1st and 2nd division | segmentation IDT part provided by doing And a first wiring line connecting the first IDT and the sixth IDT, and a first division of the third IDT. An IDT section, a second wiring line connecting a first divided IDT section of the eighth IDT, a second divided IDT section of the third IDT, and a second division of the eighth IDT A third wiring line connecting the IDT unit; and a fourth wiring line connecting the fifth IDT and the tenth IDT; and the first and third wiring lines. The first to tenth IDTs are provided such that the phase of the electrical signal transmitting the signal and the phase of the electrical signal transmitting the second and fourth wiring lines are 180 degrees different from each other. To do.

本発明に係るバランス型ＳＡＷフィルタのある特定の局面では、前記第１の縦結合共振子型ＳＡＷフィルタ部の第３のＩＤＴの前記第２の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部と、前記第２の縦結合共振子型ＳＡＷフィルタ部の第８のＩＤＴの前記第１の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部とが接地されている。   In a specific aspect of the balanced SAW filter according to the present invention, the balanced SAW filter is not connected to the second longitudinally coupled resonator type SAW filter part of the third IDT of the first longitudinally coupled resonator type SAW filter part. And the end of the eighth IDT of the second longitudinally coupled resonator type SAW filter unit that is not connected to the first longitudinally coupled resonator type SAW filter unit are grounded. Yes.

本発明に係るバランス型ＳＡＷフィルタの他の特定の局面では、前記第１の縦結合共振子型ＳＡＷフィルタ部の前記第３のＩＤＴの前記第２の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部と、前記第２の縦結合共振子型ＳＡＷフィルタ部の前記第８のＩＤＴの前記第１の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部とが、電気的に浮かされている。   In another specific aspect of the balanced SAW filter according to the present invention, the balance type SAW filter is connected to the second longitudinally coupled resonator type SAW filter part of the third IDT of the first longitudinally coupled resonator type SAW filter part. An end of the second longitudinally coupled resonator type SAW filter unit that is not connected to the first longitudinally coupled resonator type SAW filter unit of the eighth IDT. Is floating electrically.

本発明に係るバランス型ＳＡＷフィルタでは、５ＩＤＴ型の第１の縦結合共振子型ＳＡＷフィルタ部と、第２の縦結合共振子型ＳＡＷフィルタ部が二段縦続接続されている構成において、第１の縦結合共振子型ＳＡＷフィルタ部の中央の第３のＩＤＴ及び第２の縦結合共振子型ＳＡＷフィルタ部の中央の第８のＩＤＴが、それぞれ、表面波伝搬方向に沿って分割された第１，第２の分割ＩＤＴ部を有する。そして、上記第１のＩＤＴと第６のＩＤＴとを接続している第１の配線ライン、及び第３のＩＤＴの第２の分割ＩＤＴ部と、第８のＩＤＴの第２の分割ＩＤＴ部とを接続している第３の配線ラインを伝送される電気信号の位相と、第３のＩＤＴの第１の分割ＩＤＴ部と第８のＩＤＴの第１の分割ＩＤＴ部とを接続している第２の配線ライン及び第５のＩＤＴと第１０のＩＤＴとを接続している第４の配線ラインにおいて、伝送される電気信号の位相とが１８０度異なっている。
よって、第１の平衡端子に接続されているＩＤＴと、該ＩＤＴと隣り合うＩＤＴとの隣り合う最外側電極指の極性関係が、第２の平衡端子に接続されているＩＤＴと、該ＩＤＴの隣りのＩＤＴとの隣り合う最外側電極指の極性関係と同じとされているため、第１，第２の平衡端子間の平衡度が良好になる。In the balanced SAW filter according to the present invention, in a configuration in which a 5IDT type first longitudinally coupled resonator type SAW filter unit and a second longitudinally coupled resonator type SAW filter unit are cascade-connected, the first The third IDT at the center of the longitudinally coupled resonator type SAW filter part and the eighth IDT at the center of the second longitudinally coupled resonator type SAW filter part are respectively divided along the surface wave propagation direction. 1 and a second divided IDT section. A first wiring line connecting the first IDT and the sixth IDT, a second divided IDT section of the third IDT, a second divided IDT section of the eighth IDT, The phase of the electrical signal transmitted through the third wiring line connecting the first IDT unit of the third IDT and the first divided IDT unit of the eighth IDT are connected to each other. In the second wiring line and the fourth wiring line connecting the fifth IDT and the tenth IDT, the phase of the transmitted electrical signal is 180 degrees different.
Therefore, the polarity relationship between the IDT connected to the first balanced terminal and the outermost electrode finger adjacent to the IDT adjacent to the IDT is such that the IDT connected to the second balanced terminal and the IDT of the IDT Since the polarity relationship between the adjacent outermost electrode fingers with the adjacent IDT is the same, the degree of balance between the first and second balanced terminals is improved.

本発明において、第１のＳＡＷフィルタ部の第３のＩＤＴの第２の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部と、第２の縦結合共振子型ＳＡＷフィルタ部の第８のＩＤＴの第１の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部とが接地されている場合には、ＩＤＴのアースが強化され挿入損失を小さくすることができる。   In the present invention, the end of the first SAW filter unit on the side not connected to the second longitudinally coupled resonator type SAW filter unit of the third IDT, and the second longitudinally coupled resonator type SAW filter unit When the end of the eighth IDT on the side not connected to the first longitudinally coupled resonator SAW filter is grounded, the grounding of the IDT can be strengthened and insertion loss can be reduced.

前記第１の縦結合共振子型ＳＡＷフィルタ部の前記第３のＩＤＴの前記第２の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部と、前記第２の縦結合共振子型ＳＡＷフィルタ部の前記第８のＩＤＴの前記第１の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部とが、電気的に浮かされている場合には、第３，第８のＩＤＴの端部においてアースパッドを設ける必要がないので、圧電基板を小さくすることができる。   An end of the third IDT on the side not connected to the second longitudinally coupled resonator type SAW filter part of the first longitudinally coupled resonator type SAW filter part, and the second longitudinally coupled resonator If the end of the eighth IDT of the type SAW filter unit that is not connected to the first longitudinally coupled resonator type SAW filter unit is electrically floated, the third and eighth Since there is no need to provide a ground pad at the end of the IDT, the piezoelectric substrate can be made small.

図１は、本発明の一実施形態に係るバランス型ＳＡＷフィルタの模式的平面図である。FIG. 1 is a schematic plan view of a balanced SAW filter according to an embodiment of the present invention. 図２は、図１に示したバランス型ＳＡＷフィルタの減衰量周波数特性を示す図である。FIG. 2 is a diagram showing attenuation frequency characteristics of the balanced SAW filter shown in FIG. 図３は、従来のバランス型ＳＡＷフィルタの一例を示す模式的平面図である。FIG. 3 is a schematic plan view showing an example of a conventional balanced SAW filter.

符号の説明Explanation of symbols

１…バランス型ＳＡＷフィルタ
２…圧電基板
３…第１の縦結合共振子型ＳＡＷフィルタ部
４…第２の縦結合共振子型ＳＡＷフィルタ部
５…不平衡端子
６，７…第１，第２の平衡端子
１１〜１５…第１〜第５のＩＤＴ
１３ａ，１３ｂ…第１，第２の分割ＩＤＴ部
１３ｃ，１３ｄ…バスバー部
１６〜２０…第６〜第１０のＩＤＴ
１８ａ，１８ｂ…第１，第２の分割ＩＤＴ部
１８ｃ，１８ｄ…バスバー部
２１ａ，２１ｂ…反射器
２２ａ，２２ｂ…反射器
３１〜３４…第１〜第４の配線ラインDESCRIPTION OF SYMBOLS 1 ... Balance type SAW filter 2 ... Piezoelectric substrate 3 ... 1st longitudinally coupled resonator type SAW filter part 4 ... 2nd longitudinally coupled resonator type SAW filter part 5 ... Unbalanced terminals 6, 7 ... 1st, 2nd Balanced terminals 11-15 ... 1st to 5th IDT
13a, 13b ... 1st and 2nd divided IDT part 13c, 13d ... Busbar part 16-20 ... 6th-10th IDT
18a, 18b ... 1st and 2nd division | segmentation IDT part 18c, 18d ... Bus-bar part 21a, 21b ... Reflector 22a, 22b ... Reflector 31-34 ... 1st-4th wiring line

以下、図面を参照しつつ、本発明の具体的な実施形態を説明することにより、本発明を明らかにする。   Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

図１は、本発明の一実施形態に係るバランス型ＳＡＷフィルタの模式的平面図である。本実施形態のバランス型ＳＡＷフィルタ１は、ＥＧＳＭ方式の受信用帯域フィルタとして用いられるものである。なお、ＥＧＳＭ受信用帯域フィルタの通過帯域は９２５〜９６０ＭＨｚである。   FIG. 1 is a schematic plan view of a balanced SAW filter according to an embodiment of the present invention. The balanced SAW filter 1 according to the present embodiment is used as an EGSM reception band filter. The passband of the EGSM reception band filter is 925 to 960 MHz.

バランス型ＳＡＷフィルタ１は、圧電基板２を用いて構成されている。本実施形態では、圧電基板２は、４０±５°ＹカットＸ伝搬のＬｉＴａＯ3基板により構成されている。
もっとも、本発明では、圧電基板として、他の結晶角の圧電単結晶基板を用いてもよく、また、圧電セラミック基板を用いてもよい。他の圧電単結晶基板としては、例えば、６４°〜７２°ＹカットＸ伝搬のＬｉＮｂＯ3基板や４１°ＹカットＸ伝搬のＬｉＮｂＯ3基板などを挙げることができる。The balanced SAW filter 1 is configured using a piezoelectric substrate 2. In this embodiment, the piezoelectric substrate 2 is composed of a 40 ± 5 ° Y-cut X-propagation LiTaO 3 substrate.
However, in the present invention, a piezoelectric single crystal substrate having another crystal angle may be used as the piezoelectric substrate, or a piezoelectric ceramic substrate may be used. Examples of other piezoelectric single crystal substrates include a 64 ° to 72 ° Y-cut X-propagation LiNbO 3 substrate and a 41 ° Y-cut X-propagation LiNbO 3 substrate.

圧電基板２上に、後述する複数の電極を形成することにより、第１の縦結合共振子型ＳＡＷフィルタ部３と、第２の縦結合共振子型ＳＡＷフィルタ部４とが構成されている。第１，第２の縦結合共振子型ＳＡＷフィルタ部３，４は二段縦続接続されている。   A first longitudinally coupled resonator type SAW filter unit 3 and a second longitudinally coupled resonator type SAW filter unit 4 are configured by forming a plurality of electrodes to be described later on the piezoelectric substrate 2. The first and second longitudinally coupled resonator type SAW filter units 3 and 4 are cascaded in two stages.

第１の縦結合共振子型ＳＡＷフィルタ部３では、圧電基板２上に、表面波伝搬方向に沿って第１〜第５のＩＤＴ１１〜１５が配置されている。ＩＤＴ１１〜１５が設けられている領域の両側に反射器２１ａ，２１ｂが配置されている。   In the first longitudinally coupled resonator type SAW filter unit 3, first to fifth IDTs 11 to 15 are arranged on the piezoelectric substrate 2 along the surface wave propagation direction. Reflectors 21a and 21b are arranged on both sides of a region where IDTs 11 to 15 are provided.

第２のＩＤＴ１２及び第４のＩＤＴ１４の一端が共通接続されて不平衡端子５に接続されている。ＩＤＴ１２，１４の他端は接地されている。第１，第５のＩＤＴ１１，１５の一端は接地されており、他端は後述する第２の縦結合共振子型ＳＡＷフィルタ部４の第６のＩＤＴ１６及び第１０のＩＤＴ２０に電気的に接続されている。   One ends of the second IDT 12 and the fourth IDT 14 are commonly connected and connected to the unbalanced terminal 5. The other ends of the IDTs 12 and 14 are grounded. One end of each of the first and fifth IDTs 11 and 15 is grounded, and the other end is electrically connected to a sixth IDT 16 and a tenth IDT 20 of a second longitudinally coupled resonator type SAW filter unit 4 described later. ing.

中央の第３のＩＤＴ１３は、表面波伝搬方向に沿って二分割されている。すなわち、表面波伝搬方向に沿って配置された第１の分割ＩＤＴ部１３ａ及び第２の分割ＩＤＴ部１３ｂを有する。ここでは、ＩＤＴ１３の一対のバスバーの内一方のバスバーは共通されており、他方のバスバーが分割されて、分割ＩＤＴ部１３ａ，１３ｂが形成されている。すなわち、バスバーの分割により形成された一方のバスバー部１３ｃが配置されている部分が第１の分割ＩＤＴ部１３ａを構成しており、他方のバスバー部１３ｄが配置されている部分が第２の分割ＩＤＴ部１３ｂを構成している。   The center third IDT 13 is divided into two along the surface wave propagation direction. That is, it has the 1st division | segmentation IDT part 13a and the 2nd division | segmentation IDT part 13b arrange | positioned along the surface wave propagation | transmission direction. Here, one bus bar of the pair of bus bars of IDT 13 is common, and the other bus bar is divided to form divided IDT portions 13a and 13b. In other words, the portion where one bus bar portion 13c formed by dividing the bus bar constitutes the first divided IDT portion 13a, and the portion where the other bus bar portion 13d is arranged is the second divided portion. The IDT unit 13b is configured.

上記バスバー部１３ｃ，１３ｄは、第２の縦結合共振子型ＳＡＷフィルタ部４側に位置するように配置されている。   The bus bar portions 13c and 13d are arranged so as to be positioned on the second longitudinally coupled resonator type SAW filter portion 4 side.

なお、本実施形態では、第１の縦結合共振子型ＳＡＷフィルタ部３における表面波伝搬方向と、第２の縦結合共振子型ＳＡＷフィルタ部４における表面波伝搬方向とが平行とされている。   In the present embodiment, the surface wave propagation direction in the first longitudinally coupled resonator type SAW filter unit 3 is parallel to the surface wave propagation direction in the second longitudinally coupled resonator type SAW filter unit 4. .

第２の縦結合共振子型ＳＡＷフィルタ部４は、表面波伝搬方向に沿って配置された第６〜第１０のＩＤＴ１６〜２０を有する。ＩＤＴ１６〜２０が設けられている領域の表面波伝搬方向両側に反射器２２ａ，２２ｂが配置されている。前述したように、第６及び第１０のＩＤＴ１６，２０の一端が、それぞれ、第１，第４の配線ライン３１，３４により、第１，第５のＩＤＴ１１，１５に電気的に接続されている。   The second longitudinally coupled resonator-type SAW filter unit 4 includes sixth to tenth IDTs 16 to 20 arranged along the surface wave propagation direction. Reflectors 22a and 22b are arranged on both sides of the surface wave propagation direction in the region where the IDTs 16 to 20 are provided. As described above, one ends of the sixth and tenth IDTs 16 and 20 are electrically connected to the first and fifth IDTs 11 and 15 by the first and fourth wiring lines 31 and 34, respectively. .

他方、第７，第９のＩＤＴ１７，１９の各一端は接地されており、他端が、それぞれ、第１の平衡端子６及び第２の平衡端子７に電気的に接続されている。すなわち、バランス型ＳＡＷフィルタ１は、不平衡端子５と、第１，第２の平衡端子６，７とを有する平衡−不平衡変換機能を有するバランス型ＳＡＷフィルタである。   On the other hand, one end of each of the seventh and ninth IDTs 17 and 19 is grounded, and the other end is electrically connected to the first balanced terminal 6 and the second balanced terminal 7, respectively. That is, the balanced SAW filter 1 is a balanced SAW filter having a balanced-unbalanced conversion function including the unbalanced terminal 5 and the first and second balanced terminals 6 and 7.

第８のＩＤＴ１８は、第３のＩＤＴ１３と同様に、表面波伝搬方向に二分割されている。すなわち、ＩＤＴ１８は、第１，第２の分割ＩＤＴ部１８ａ，１８ｂを有する。ここでも、一方のバスバーを二分割することにより、分割ＩＤＴ部１８ａ，１８ｂが構成されている。   As with the third IDT 13, the eighth IDT 18 is divided into two in the surface wave propagation direction. That is, the IDT 18 includes first and second divided IDT units 18a and 18b. Again, the divided IDT sections 18a and 18b are configured by dividing one bus bar into two.

第１の分割ＩＤＴ部１８ａのバスバー部１８ｃと、第２の分割ＩＤＴ部１８ｂのバスバー部１８ｄとが図示のようにギャップを隔てて分離されている。上記バスバー部１８ｃ，１８ｄは、ＩＤＴ１８において第１の縦結合共振子型ＳＡＷフィルタ部３側に配置されている。   The bus bar portion 18c of the first divided IDT portion 18a and the bus bar portion 18d of the second divided IDT portion 18b are separated with a gap as shown in the figure. The bus bar portions 18c and 18d are arranged on the IDT 18 on the first longitudinally coupled resonator type SAW filter portion 3 side.

言い換えれば、ＩＤＴ１３と、ＩＤＴ１８とは、第１，第２の縦結合共振子型ＳＡＷフィルタ部３，４間のスペースを隔てて、バスバー部１３ｃ，１３ｄと、バスバー部１８ｃ，１８ｄとが対向するように配置されている。そして、第３のＩＤＴ１３の第１の分割ＩＤＴ部１３ａが、第２の配線ライン３２により、第８のＩＤＴの第１の分割ＩＤＴ部１８ａに電気的に接続されている。また、第３のＩＤＴの第２の分割ＩＤＴ部１３ｂが、第３の配線ライン３３により、第８のＩＤＴの第２の分割ＩＤＴ部１８ｂに電気的に接続されている。   In other words, in the IDT 13 and the IDT 18, the bus bar portions 13c and 13d and the bus bar portions 18c and 18d face each other with a space between the first and second longitudinally coupled resonator type SAW filter portions 3 and 4. Are arranged as follows. The first divided IDT portion 13 a of the third IDT 13 is electrically connected to the first divided IDT portion 18 a of the eighth IDT by the second wiring line 32. Further, the second divided IDT portion 13 b of the third IDT is electrically connected to the second divided IDT portion 18 b of the eighth IDT by the third wiring line 33.

上記ＩＤＴ１１〜１５，１６〜２０、反射器２１ａ，２１ｂ，２２ａ，２２ｂ及び配線ライン３１〜３４は、適宜の電極材料を用いて形成され得るが、本実施形態では、Ａｌにより形成されている。   The IDTs 11 to 15, 16 to 20, the reflectors 21a, 21b, 22a, and 22b and the wiring lines 31 to 34 can be formed using appropriate electrode materials, but in this embodiment, they are formed of Al.

なお、本実施形態では、ＩＤＴ同士が隣り合う部分において双方のＩＤＴの端部に狭ピッチ電極指部Ｎが形成されている。例えば、ＩＤＴ１１とＩＤＴ１２とが隣り合う部分では、ＩＤＴ１１のＩＤＴ１２側端部近傍の複数本の電極指のピッチが、残りの電極指のピッチよりも小さくされている。この相対的にピッチが小さい複数の電極指が設けられている部分が、狭ピッチ電極指部Ｎである。   In the present embodiment, narrow pitch electrode finger portions N are formed at the end portions of both IDTs in a portion where the IDTs are adjacent to each other. For example, in the portion where IDT 11 and IDT 12 are adjacent, the pitch of the plurality of electrode fingers in the vicinity of the IDT 12 side end portion of IDT 11 is made smaller than the pitch of the remaining electrode fingers. A portion where the plurality of electrode fingers having a relatively small pitch is provided is a narrow pitch electrode finger portion N.

従って、ＩＤＴ１３では、両側にＩＤＴ１２，１４が配置されているため、ＩＤＴ１３では、ＩＤＴ１２側端部及びＩＤＴ１４側端部の双方の狭ピッチ電極指部Ｎが設けられている。他のＩＤＴ同士が隣り合っている部分においても、双方のＩＤＴに狭ピッチ電極指部Ｎが設けられている。   Accordingly, since IDTs 12 and 14 are arranged on both sides of IDT 13, narrow ID electrode fingers N at both the IDT 12 side end and the IDT 14 side end are provided at IDT 13. Even in a portion where other IDTs are adjacent to each other, narrow pitch electrode finger portions N are provided on both IDTs.

狭ピッチ電極指部Ｎを設けることにより、ＩＤＴ間の不連続性を緩和することができる。また、縦結合共振子型ＳＡＷフィルタ部３，４では、帯域特性を得るために、一次モード及び三次モードと、ＩＤＴとＩＤＴとの間の間隔に依存する共振点を有する共振モードの３つの共振モードを結合することにより得られている。上記狭ピッチ電極指部Ｎを設けることにより、さらにＩＤＴ間の間隔を調整することにより、広帯域のフィルタ特性を得ることができる。もっとも、本発明においては、狭ピッチ電極指部Ｎは必ずしも設けられずともよい。   By providing the narrow pitch electrode finger N, the discontinuity between IDTs can be reduced. Further, in the longitudinally coupled resonator type SAW filter units 3 and 4, in order to obtain band characteristics, three resonances of a resonance mode having a resonance point depending on the interval between the IDT and the IDT and the primary mode and the tertiary mode. It is obtained by combining modes. By providing the narrow pitch electrode finger portion N, and further adjusting the interval between the IDTs, a broadband filter characteristic can be obtained. However, in the present invention, the narrow pitch electrode finger N is not necessarily provided.

不平衡端子５におけるインピーダンスは５０Ω、平衡端子６，７におけるインピーダンスは、１５０Ωとなるように設定されている。   The impedance at the unbalanced terminal 5 is set to 50Ω, and the impedance at the balanced terminals 6 and 7 is set to 150Ω.

本実施形態の特徴は、上記第１，第３の配線ライン３１，３３を伝送する電気信号の位相に対し、第２，第４の配線ライン３２，３４を伝送する信号の位相が１８０度異なるように、ＩＤＴ１１〜１５，１６〜２０が配置されていることにある。それによって、第１，第２の縦結合共振子型ＳＡＷフィルタ部３，４を二段縦続接続したバランス型ＳＡＷフィルタ１において、第１，第２の平衡端子６，７に伝送される電気信号における直達波に由来する成分を著しく小さくすることが可能となる。   The feature of this embodiment is that the phase of the signal transmitted through the second and fourth wiring lines 32 and 34 is 180 degrees different from the phase of the electrical signal transmitted through the first and third wiring lines 31 and 33. Thus, IDTs 11 to 15 and 16 to 20 are arranged. As a result, in the balanced SAW filter 1 in which the first and second longitudinally coupled resonator type SAW filter units 3 and 4 are cascade-connected, the electric signal transmitted to the first and second balanced terminals 6 and 7. It is possible to significantly reduce the component derived from the direct wave at.

従って、平衡端子６，７から出力される信号を、例えば後段に接続される平衡型ミキサーＩＣにより差動増幅した場合、該ミキサーＩＣから出力される信号における同相信号の位相を極めて小さくすることが可能となる。これを具体的な実験例に基づき説明する。   Therefore, when the signals output from the balanced terminals 6 and 7 are differentially amplified, for example, by a balanced mixer IC connected to the subsequent stage, the phase of the in-phase signal in the signal output from the mixer IC is made extremely small. Is possible. This will be described based on a specific experimental example.

以下の要領で、圧電基板２上に、ＩＤＴ１１〜１５及び反射器２１ａ，２１ｂを形成した。   The IDTs 11 to 15 and the reflectors 21a and 21b were formed on the piezoelectric substrate 2 in the following manner.

電極指交叉幅：１５０μｍ
ＩＤＴ１１〜１５の電極指の本数：ＩＤＴ１１〜１５の順に２５（４）／（４）２８（４）／（４）４２（４）／（４）２８（４）／（４）２５。但し、括弧内は狭ピッチ電極指部Ｎにおける電極指の本数であり、括弧外の本数は狭ピッチ電極指部以外の電極指の本数を意味するものとする。例えば、ＩＤＴ１１は、２５（４）であるため、狭ピッチ電極指部以外の２５本の電極指と、４本の電極指からなる狭ピッチ電極指部を有することを意味し、ＩＤＴ１２では、一方端部に４本の電極指を有する狭ピッチ電極指部Ｎを有し、中央に２８本の電極指を有し、反対側の端部に４本の電極指を有する狭ピッチ電極指部が構成されていることを意味する。Electrode finger crossing width: 150 μm
Number of electrode fingers of IDTs 11 to 15: 25 (4) / (4) 28 (4) / (4) 42 (4) / (4) 28 (4) / (4) 25 in the order of IDTs 11-15. However, the number in the parentheses is the number of electrode fingers in the narrow pitch electrode finger portion N, and the number outside the parentheses means the number of electrode fingers other than the narrow pitch electrode finger portion. For example, since IDT11 is 25 (4), it means that it has 25 electrode fingers other than the narrow pitch electrode finger portion and a narrow pitch electrode finger portion consisting of four electrode fingers. There is a narrow pitch electrode finger portion having a narrow pitch electrode finger portion N having four electrode fingers at the end portion, having 28 electrode fingers at the center and four electrode fingers at the opposite end portion. Means that it is configured.

反射器の電極指の本数：８０本
メタライゼーションレシオ：０．７０
電極膜厚：０．０８２λＩ（但し、λＩは、狭ピッチ電極指部Ｎ以外の電極指のピッチで定まる波長）Number of reflector electrode fingers: 80 Metallization ratio: 0.70
Electrode film thickness: 0.082λI (where λI is a wavelength determined by the pitch of electrode fingers other than the narrow pitch electrode finger portion N)

なお、第２の縦結合共振子型ＳＡＷフィルタ部４のＩＤＴ１６〜２０及び反射器２２ａ，２２ｂの仕様は、第１の縦結合共振子型ＳＡＷフィルタ部３のＩＤＴ１１〜１５及び反射器２１ａ，２１ｂの仕様と同様とした。   The specifications of the IDTs 16 to 20 and the reflectors 22a and 22b of the second longitudinally coupled resonator type SAW filter unit 4 are the IDTs 11 to 15 and the reflectors 21a and 21b of the first longitudinally coupled resonator type SAW filter unit 3. The same as the specification.

もっとも、図１に示されているように、ＩＤＴ１１〜１３，１５と、第２の縦結合共振子型ＳＡＷフィルタ部４のＩＤＴ１６〜１８，２０とは、縦結合共振子型ＳＡＷフィルタ部３，４間の中心を通り、表面波伝搬方向と平行に延びる仮想中心線を介して対称に構成されている。なお、第４のＩＤＴ１４と、第９のＩＤＴ１９とは、上記仮想中心線を介して対称とはされていない。   However, as shown in FIG. 1, the IDTs 11 to 13 and 15 and the IDTs 16 to 18 and 20 of the second longitudinally coupled resonator type SAW filter unit 4 are the longitudinally coupled resonator type SAW filter units 3 and 3. It is configured symmetrically through a virtual center line that passes through the center between the four and extends parallel to the surface wave propagation direction. The fourth IDT 14 and the ninth IDT 19 are not symmetric with respect to the virtual center line.

上記のようにして構成された本実施形態のバランス型ＳＡＷフィルタ１の減衰量周波数特性を図２に示す。図２に示すように、通過帯域内の最大挿入損失は１．６６ｄＢと小さかった。   FIG. 2 shows the attenuation frequency characteristics of the balanced SAW filter 1 of the present embodiment configured as described above. As shown in FIG. 2, the maximum insertion loss in the pass band was as small as 1.66 dB.

本実施形態の縦結合共振子型ＳＡＷフィルタでは、上記のように通過帯域内の挿入損失を低減することができる。
また、例えば、図１において、ＩＤＴ１６とＩＤＴ１７との隣り合う最外電極指の極性は−と＋、ＩＤＴ１７とＩＤＴ１８とでは−と−、ＩＤＴ１８とＩＤＴ１９とでは−と−、ＩＤＴ１９とＩＤＴ２０とでは＋と−となる。
従って、第１の平衡端子６に接続されているＩＤＴ１６，１８と、該ＩＤＴ１６，１８と隣り合うＩＤＴ１７との隣り合う最外側電極指の極性関係が、第２の平衡端子７に接続されているＩＤＴ１８，２０と、該ＩＤＴ１８，２０の隣りのＩＤＴ１９との隣り合う最外側電極指の極性関係と同じとされているため、第１，第２の平衡端子６，７間の平衡度が良好になる。In the longitudinally coupled resonator type SAW filter of the present embodiment, the insertion loss in the passband can be reduced as described above.
Further, for example, in FIG. 1, the polarities of adjacent outermost electrode fingers of IDT 16 and IDT 17 are − and +, − and − in IDT 17 and IDT 18, − and − in IDT 18 and IDT 19, and + in IDT 19 and IDT 20. And-.
Therefore, the polarity relationship of the adjacent outermost electrode fingers of the IDTs 16 and 18 connected to the first balanced terminal 6 and the IDTs 17 adjacent to the IDTs 16 and 18 is connected to the second balanced terminal 7. Since the polarity relationship between the adjacent outermost electrode fingers of the IDTs 18 and 20 and the IDT 19 adjacent to the IDTs 18 and 20 is the same, the balance between the first and second balanced terminals 6 and 7 is excellent. Become.

なお、上記実施形態では、第３のＩＤＴ１３の第２の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部と、第８のＩＤＴ１８の第１の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部とが接地されていたが、これらの端部は電気的に浮かされていてもよい。上記各端部が電気的に浮かされている場合には、第３，第８のＩＤＴの端部においてアースパッドを設ける必要がないので、圧電基板を小さくすることができる。   In the above embodiment, the end of the third IDT 13 on the side not connected to the second longitudinally coupled resonator type SAW filter unit and the first longitudinally coupled resonator type SAW filter unit of the eighth IDT 18 Although the end portions on the side not connected to the ground are grounded, these end portions may be electrically floated. When each of the end portions is electrically floated, it is not necessary to provide a ground pad at the end portions of the third and eighth IDTs, so that the piezoelectric substrate can be made small.

Claims (3)

不平衡端子と、第１，第２の平衡端子とを有するバランス型ＳＡＷフィルタであって、
圧電基板と、
前記圧電基板上に形成されており、表面波伝搬方向に沿って配置された第１〜第５のＩＤＴとを備え、前記第２，第４のＩＤＴが不平衡端子に接続されており、中央の第３のＩＤＴが、一対のバスバーの内の一方のバスバーを分割することにより設けられた第１，第２の分割ＩＤＴ部を有する第１の縦結合共振子型ＳＡＷフィルタ部と、
前記圧電基板上において、表面波伝搬方向に沿って配置された第６〜第１０のＩＤＴを有し、前記第７，第９のＩＤＴがそれぞれ第１，第２の平衡端子に接続されており、中央の第８のＩＤＴが、一対のバスバーの内の一方のバスバーを分割することにより設けられた第１，第２の分割ＩＤＴ部を有する第２の縦結合共振子型ＳＡＷフィルタ部とを備え、
前記第１のＩＤＴと、第６のＩＤＴとを接続している第１の配線ラインと、
前記第３のＩＤＴの第１の分割ＩＤＴ部と、第８のＩＤＴの第１の分割ＩＤＴ部を接続している第２の配線ラインと、
前記第３のＩＤＴの第２の分割ＩＤＴ部と、第８のＩＤＴの第２の分割ＩＤＴ部とを接続している第３の配線ラインと、
前記第５のＩＤＴと第１０のＩＤＴとを接続している第４の配線ラインとをさらに備え、
前記第１，第３の配線ラインを伝送している電気信号の位相と、前記第２，第４の配線ラインを伝送する電気信号の位相とが１８０度異なるように第１〜第１０のＩＤＴが設けられていることを特徴とする、バランス型ＳＡＷフィルタ。A balanced SAW filter having an unbalanced terminal and first and second balanced terminals,
A piezoelectric substrate;
The first to fifth IDTs formed along the surface wave propagation direction are formed on the piezoelectric substrate, and the second and fourth IDTs are connected to an unbalanced terminal, A first longitudinally coupled resonator type SAW filter section having first and second divided IDT sections provided by dividing one bus bar of a pair of bus bars;
The piezoelectric substrate has sixth to tenth IDTs arranged along the surface wave propagation direction, and the seventh and ninth IDTs are connected to the first and second balanced terminals, respectively. A second longitudinally coupled resonator type SAW filter section having first and second divided IDT sections provided by dividing one of the pair of bus bars by an eighth IDT in the center. Prepared,
A first wiring line connecting the first IDT and the sixth IDT;
A second wiring line connecting the first divided IDT portion of the third IDT and the first divided IDT portion of the eighth IDT;
A third wiring line connecting the second divided IDT portion of the third IDT and the second divided IDT portion of the eighth IDT;
A fourth wiring line connecting the fifth IDT and the tenth IDT;
The first to tenth IDTs so that the phase of the electrical signal transmitted through the first and third wiring lines differs from the phase of the electrical signal transmitted through the second and fourth wiring lines by 180 degrees. A balanced SAW filter is provided. 前記第１の縦結合共振子型ＳＡＷフィルタ部の第３のＩＤＴの前記第２の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部と、前記第２の縦結合共振子型ＳＡＷフィルタ部の第８のＩＤＴの前記第１の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部とが接地されていることを特徴とする、請求項１に記載のバランス型ＳＡＷフィルタ。  The end of the third IDT of the first longitudinally coupled resonator-type SAW filter part that is not connected to the second longitudinally-coupled resonator-type SAW filter part, and the second longitudinally-coupled resonator type 2. The balanced type according to claim 1, wherein an end of the eighth IDT of the SAW filter unit that is not connected to the first longitudinally coupled resonator type SAW filter unit is grounded. 3. SAW filter. 前記第１の縦結合共振子型ＳＡＷフィルタ部の前記第３のＩＤＴの前記第２の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部と、前記第２の縦結合共振子型ＳＡＷフィルタ部の前記第８のＩＤＴの前記第１の縦結合共振子型ＳＡＷフィルタ部に接続されていない側の端部とが、電気的に浮かされていることを特徴とする、請求項１に記載のバランス型ＳＡＷフィルタ。  An end of the third IDT on the side not connected to the second longitudinally coupled resonator type SAW filter part of the first longitudinally coupled resonator type SAW filter part, and the second longitudinally coupled resonator 2. An end of the eighth IDT of the type SAW filter unit that is not connected to the first longitudinally coupled resonator type SAW filter unit is electrically floated. The balanced SAW filter described in 1.
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